"Spontaneous" loss of the plastid system in the protozoan Euglena gracilis following transfer from organic to defined medium has been shown to be due to an inhibitory action of alcohol (as carbon source) on replication of the plastids. As a first step in elucidating the mechanism of alcohol action we plan to study the effect of low concentrations of alcohol on DNA, RNA, and protein synthesis in isolated chloroplasts. It has been found that pH-dependent photo-inhibition of division in non-photosynthetic Euglena is expressed only when fumarate, ethanol or butanol serve as carbon source. This suggests that light retards incorporation of these compounds in the effective pH range. We plan to examine the effect of pH and light on incorporation of these compounds, and possibly to demonstrate inactivation of carriers by light over certain pH ranges.